Conventional vertical takeoff and landing aircraft (VTOL) usually include engines which are mounted at the sides of the fuselage or the underside of the wings. There are VTOL's having engines which can be pivoted about the pitch axis or about an axis parallel to the pitch axis for vertical takeoffs. Examples of this type of aircraft include U.S. Pat. Nos. 3,388,878 and 3,084,888. In U.S. Pat. No. 3,084,888 a VTOL aircraft having lifting jets which can be swiveled from within the fuselage to longitudinal sides thereof for vertically lifting the aircraft is disclosed. After having vertically lifted off, the lift jets are returned within the fuselage and different jets are used for the horizontal flight. Similarly, the VTOL aircraft of U.S. Pat. No. 3,388,878 utilizes movable vertical lift-off engines which are used strictly for vertical lift-offs.
VTOL aircraft using both vertical lift-off engines and cruise engines are also known. Examples of this type of VTOL aircraft include U.S. Pat. Nos. 3,042,342, 3,972,490, 3,460,783 and 3,387,456. In U.S. Pat. No. 3,042,342, four small gas turbine engines are positioned in the midsection of the aircraft for providing the vertical lift thrust, while a cruise engine is mounted to the aft section of the aircraft. In U.S. Pat. No. 3,972,490, two turbines and three high bypass turbotip fans are disposed in the fuselage of the aircraft to produce vertical lift and cruise for the same. One of the turbotip fans is located in the fore section of the aircraft while the remaining two turbotip fans are situated in the aft section of the aircraft. Likewise, in U.S. Pat. No. 3,387,456, vertical lift engines are shown to be situated in the front and midsection of the aircraft while cruise engines are located in the aft section of the same. In U.S. Pat. No. 3,460,783, a VTOL aircraft having front rotatable parallel engines adjacent to opposite sides of the fuselage for providing thrust for vertical lift-offs and cruising is disclosed. Further disclosed in U.S. Pat. No. 3,460,783 are fixed stern engines which, together with afterburners and deflection exhaust pipes, are used for maintaining control of the aircraft during vertical lift-offs. The U.S. Pat. No. 3,460,783 reference teaches that by using both the stern engines and the front rotatable engines, the control of the aircraft is maintained during lift-offs. Both the front rotatable engines and the stern engines are fully utilized for balancing the moments of the aircraft about its pitch axis. Needless to say, a large amount of fuel has to be expended during vertical lift-offs by the U.S. Pat. No. 3,460,783 aircraft, as no interactive thrust or interaction between the exhaust from the front and stern engines is provided.